This invention generally relates to a print control system and more particularly to a print control system suitable for improving accuracy of aligning portions of a vertical rule or portions of a vertically enlarged letter and thus promoting print quality when these portions are printed bidirectionally.
When portions of a vertical rule extending across a plurality of lines or portions of a vertically enlarged letter extending across two lines are printed bidirectionally, conventional printers inevitably suffer from a displacement or misalignment of printing position between a portion on the preceding line and another portion on the succeeding line because a conveying mechanism for a printing head has a mechanical factor such as backlash. Conventionally, to correct the misalignment, the timing for commencement of printing in the positive or negative direction is controlled for acceleration or retardation by using, for example, a microprogram. The conventional control for the purpose of correction of the printing position is however performed solely in a unit of dot pitch with the result that the correction is invalidated for an amount of misalignment being smaller than half the dot pitch. Accordingly, when portions of a vertical rule or a vertically enlarged letter are printed bidirectionally, accuracy of alignment is impaired and print quality is degraded. To improve print quality, printing is therefore performed unidirectionally at the cost of throughput in printing for documents containing vertical rules and vertically enlarged letters.
When viewing with the naked eye, degradation in print quality may be intuited when there occurs a displacement of about 0.07 mm or more for a dot diameter of 0.2 mm and a dot pitch of 1/180 inches, the displacement amounting to half the dot pitch at the minimum.
A relevant printer of this type is disclosed in, for example, JP-A-55-37653.